Systems, methods and devices for endometrial ablation utilizing radio frequency

ABSTRACT

Methods, systems and devices for endometrial ablation. In accordance with a method, a working end of an RF ablation device is positioned in a patient uterus to contact endometrial tissue, the working end comprising a dielectric. Radiofrequency energy is applied for a first interval of time at constant power, the power being sufficient to capacitively couple current across the dielectric to the contacted endometrial tissue. A voltage parameter measured within the first interval, and radiofrequency energy is applied at a constant voltage over a second, treatment interval to ablate endometrial tissue, the constant voltage being related to the recorded voltage.

BACKGROUND

1. Field of the Invention

The present invention relates to electrosurgical methods and devices forglobal endometrial ablation in a treatment of menorrhagia. Moreparticularly, the present invention relates to applying radiofrequencycurrent to endometrial tissue by means of capacitively coupling thecurrent through an expandable, thin-wall dielectric member enclosing anionized gas.

A variety of devices have been developed or proposed for endometrialablation. Of relevance to the present invention, a variety ofradiofrequency ablation devices have been proposed including solidelectrodes, balloon electrodes, metalized fabric electrodes, and thelike. While often effective, many of the prior electrode designs havesuffered from one or more deficiencies, such as relatively slowtreatment times, incomplete treatments, non-uniform ablation depths, andrisk of injury to adjacent organs.

For these reasons, it would be desirable to provide systems and methodsthat allow for endometrial ablation using radiofrequency current whichis rapid, provides for controlled ablation depth and which reduce therisk of injury to adjacent organs. At least some of these objectiveswill be met by the invention described herein.

2. Description of the Background Art

U.S. Pat. Nos. 5,769,880; 6,296,639; 6,663,626; and 6,813,520 describeintrauterine ablation devices formed from a permeable mesh definingelectrodes for the application of radiofrequency energy to ablateuterine tissue. U.S. Pat. No. 4,979,948 describes a balloon filled withan electrolyte solution for applying radiofrequency current to a mucosallayer via capacitive coupling. US 2008/097425, having commoninventorship with the present application, describes delivering apressurized flow of a liquid medium which carries a radiofrequencycurrent to tissue, where the liquid is ignited into a plasma as itpasses through flow orifices. U.S. Pat. No. 5,891,134 describes aradiofrequency heater within an enclosed balloon. U.S. Pat. No.6,041,260 describes radiofrequency electrodes distributed over theexterior surface of a balloon which is inflated in a body cavity to betreated. U.S. Pat. No. 7,371,231 and US 2009/054892 describe aconductive balloon having an exterior surface which acts as an electrodefor performing endometrial ablation. U.S. Pat. No. 5,191,883 describesbipolar heating of a medium within a balloon for thermal ablation. U.S.Pat. No. 6,736,811 and U.S. Pat. No. 5,925,038 show an inflatableconductive electrode.

BRIEF SUMMARY

The present invention provides methods, systems and devices forevaluating the integrity of a uterine cavity. The uterine cavity may beperforated or otherwise damaged by the transcervical introduction ofprobes and instruments into the uterine cavity. If the uterine wall isperforated, it would be preferable to defer any ablation treatment untilthe uterine wall is healed. A method of the invention comprisesintroducing transcervically a probe into a patient's uterine cavity,providing a flow of a fluid (e.g., CO₂) through the probe into theuterine cavity and monitoring the rate of the flow to characterize theuterine cavity as perforated or non-perforated based on a change in theflow rate. If the flow rate drops to zero or close to zero, thisindicates that the uterine cavity is intact and not perforated. If theflow rate does not drop to zero or close to zero, this indicates that afluid flow is leaking through a perforation in the uterine cavity intothe uterine cavity or escaping around an occlusion balloon that occludesthe cervical canal.

In accordance with embodiments, methods, systems and devices areprovided for endometrial ablation. In accordance with a method, aworking end of an RF ablation device is positioned in a patient uterusto contact endometrial tissue, the working end comprising a dielectric.Radiofrequency energy is applied for a first interval of time atconstant power, the power being sufficient to capacitively couplecurrent across the dielectric to the contacted endometrial tissue. Avoltage parameter measured within the first interval, and radiofrequencyenergy is applied at a constant voltage over a second, treatmentinterval to ablate endometrial tissue, the constant voltage beingrelated to the recorded voltage.

The first interval may be, as examples, less than 15 seconds, less than10 seconds, or less than 5 seconds.

In embodiments, the voltage parameter comprises a recorded voltagemeasured at a single point in time during the first interval, multiplerecorded voltages taken during the first interval and averaged, a rateof change of voltage over the first interval, and/or a change in voltageover the first interval.

In embodiments, the constant voltage is equal to the voltage parameter,but it may be greater than the voltage parameter, or less than thevoltage parameter. The constant voltage may include a ramp-up of voltageor a ramp-down of voltage.

In further embodiments, a method of endometrial ablation is provided,comprising positioning a working end of an RF ablation device in apatient uterus to contact endometrial tissue in the uterus; applyingradiofrequency energy at constant power during a first time interval;recording an electrical parameter within the first time interval; andapplying radiofrequency energy at a constant voltage over a second,treatment time interval to ablate endometrial tissue, the constantvoltage being derived from the electrical parameter. The electricalparameter may be, for example, a voltage parameter.

In further embodiments, an electrosurgical method is provided forendometrial ablation, including positioning a RF ablation device incontact with endometrial tissue in a patient; applying radiofrequencyenergy in a first mode at constant power over a first interval; andapplying radiofrequency energy in a second mode over a second intervalto ablate endometrial tissue, the energy level of the second mode beingdetermined based on an electrical parameter obtained from the firstmode.

In still further embodiments, an electrosurgical system for endometrialablation is provided, comprising a radiofrequency ablation devicecoupled to an radiofrequency power supply; and a controller connected tothe radiofrequency power supply and configured to operate theradiofrequency power supply by switching the application ofradiofrequency energy to the ablation device between a first, constantpower mode and a second, constant voltage mode. The controller may beconfigured to (i) apply radiofrequency energy in the first mode (ii)record a voltage parameter during the first, and (iii) appliesradiofrequency energy in the second mode at constant voltage related tothe recorded voltage parameter.

In still further embodiments, an electrosurgical system is provided forendometrial ablation, comprising a radiofrequency ablation devicecoupled to an RF power supply; control means connected to theradiofrequency power supply for switching the application ofradiofrequency energy to the ablation device between a constant powermode and a variable power mode. The control means may, for example,operate the variable power mode to maintain a constant voltage.

In still more embodiments, an electrosurgical system for endometrialablation is provided, comprising an ablation device configured forpositioning in a uterine cavity, the ablation device comprising adielectric for contacting endometrial tissue; a radiofrequency powersupply coupled to the ablation device; a system for recording anelectrical parameter of the ablation device and contacted tissue; and afeedback system coupled to the radiofrequency power supply for varyingthe application of radiofrequency energy provided by the radiofrequencypower supply to the ablation device between a constant power mode and aconstant voltage mode, the constant voltage mode being based on anelectrical parameter measured by the system for recording during theconstant power mode.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may becarried out in practice, some preferred embodiments are next described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which like reference characters denote correspondingfeatures consistently throughout similar embodiments in the attacheddrawings.

FIG. 1 is a perspective view of an ablation system corresponding to theinvention, including a hand-held electrosurgical device for endometrialablation, RF power source, gas source and controller.

FIG. 2 is a view of the hand-held electrosurgical device of FIG. 1 witha deployed, expanded thin-wall dielectric structure.

FIG. 3 is a block diagram of components of one electrosurgical systemcorresponding to the invention.

FIG. 4 is a block diagram of the gas flow components of theelectrosurgical system of FIG. 1.

FIG. 5 is an enlarged perspective view of the expanded thin-walldielectric structure, showing an expandable-collapsible frame with thethin dielectric wall in phantom view.

FIG. 6 is a partial sectional view of the expanded thin-wall dielectricstructure of FIG. 5 showing (i) translatable members of theexpandable-collapsible frame a that move the structure between collapsedand (ii) gas inflow and outflow lumens.

FIG. 7 is a sectional view of an introducer sleeve showing variouslumens of the introducer sleeve taken along line 7-7 of FIG. 6.

FIG. 8A is an enlarged schematic view of an aspect of a method of theinvention illustrating the step introducing an introducer sleeve into apatient's uterus.

FIG. 8B is a schematic view of a subsequent step of retracting theintroducer sleeve to expose a collapsed thin-wall dielectric structureand internal frame in the uterine cavity.

FIG. 8C is a schematic view of subsequent steps of the method,including, (i) actuating the internal frame to move the a collapsedthin-wall dielectric structure to an expanded configuration, (ii)inflating a cervical-sealing balloon carried on the introducer sleeve,and (iii) actuating gas flows and applying RF energy tocontemporaneously ionize the gas in the interior chamber and causecapacitive coupling of current through the thin-wall dielectricstructure to cause ohmic heating in the engaged tissue indicated bycurrent flow paths.

FIG. 8D is a schematic view of a subsequent steps of the method,including: (i) advancing the introducer sleeve over the thin-walldielectric structure to collapse it into an interior bore shown inphantom view, and (ii) withdrawing the introducer sleeve and dielectricstructure from the uterine cavity.

FIG. 9 is a cut-away perspective view of an alternative expandedthin-wall dielectric structure similar to that of FIGS. 5 and 6 show analternative electrode configuration.

FIG. 10 is an enlarged cut-away view of a portion of the expandedthin-wall dielectric structure of FIG. 9 showing the electrodeconfiguration.

FIG. 11 is a diagram of a radiofrequency energy delivery apparatus andmethod corresponding to the invention.

DETAILED DESCRIPTION

In general, an electrosurgical ablation system is described herein thatcomprises an elongated introducer member for accessing a patient'suterine cavity with a working end that deploys an expandable thin-walldielectric structure containing an electrically non-conductive gas as adielectric. In one embodiment, an interior chamber of the thin-walldielectric structure contains a circulating neutral gas such as argon.An RF power source provides current that is coupled to the neutral gasflow by a first polarity electrode disposed within the interior chamberand a second polarity electrode at an exterior of the working end. Thegas flow, which is converted to a conductive plasma by an electrodearrangement, functions as a switching mechanism that permits currentflow to engaged endometrial tissue only when the voltage across thecombination of the gas, the thin-wall dielectric structure and theengaged tissue reaches a threshold that causes capacitive couplingacross the thin-wall dielectric material. By capacitively couplingcurrent to tissue in this manner, the system provides a substantiallyuniform tissue effect within all tissue in contact with the expandeddielectric structure. Further, the invention allows the neutral gas tobe created contemporaneously with the capacitive coupling of current totissue.

In general, this disclosure may use the terms “plasma,” “conductive gas”and “ionized gas” interchangeably. A plasma consists of a state ofmatter in which electrons in a neutral gas are stripped or “ionized”from their molecules or atoms. Such plasmas can be formed by applicationof an electric field or by high temperatures. In a neutral gas,electrical conductivity is non-existent or very low. Neutral gases actas a dielectric or insulator until the electric field reaches abreakdown value, freeing the electrons from the atoms in an avalancheprocess thus forming a plasma. Such a plasma provides mobile electronsand positive ions, and acts as a conductor which supports electriccurrents and can form spark or arc. Due to their lower mass, theelectrons in a plasma accelerate more quickly in response to an electricfield than the heavier positive ions, and hence carry the bulk of thecurrent.

FIG. 1 depicts one embodiment of an electrosurgical ablation system 100configured for endometrial ablation. The system 100 includes a hand-heldapparatus 105 with a proximal handle 106 shaped for grasping with ahuman hand that is coupled to an elongated introducer sleeve 110 havingaxis 111 that extends to a distal end 112. The introducer sleeve 110 canbe fabricated of a thin-wall plastic, composite, ceramic or metal in around or oval cross-section having a diameter or major axis ranging fromabout 4 mm to 8 mm in at least a distal portion of the sleeve thataccesses the uterine cavity. The handle 106 is fabricated of anelectrically insulative material such as a molded plastic with apistol-grip having first and second portions, 114 a and 114 b, that canbe squeezed toward one another to translate an elongated translatablesleeve 115 which is housed in a bore 120 in the elongated introducersleeve 110. By actuating the first and second handle portions, 114 a and114 b, a working end 122 can be deployed from a first retracted position(FIG. 1) in the distal portion of bore 120 in introducer sleeve 110 toan extended position as shown in FIG. 2. In FIG. 2, it can be seen thatthe first and second handle portions, 114 a and 114 b, are in a secondactuated position with the working end 122 deployed from the bore 120 inintroducer sleeve 110.

FIGS. 2 and 3 shows that ablation system 100 includes an RF energysource 130A and RF controller 130B in a control unit 135. The RF energysource 130A is connected to the hand-held device 105 by a flexibleconduit 136 with a plug-in connector 137 configured with a gas inflowchannel, a gas outflow channel, and first and second electrical leadsfor connecting to receiving connector 138 in the control unit 135. Thecontrol unit 135, as will be described further below in FIGS. 3 and 4,further comprises a neutral gas inflow source 140A, gas flow controller140B and optional vacuum or negative pressure source 145 to providecontrolled gas inflows and gas outflows to and from the working end 122.The control unit 135 further includes a balloon inflation source 148 forinflating an expandable sealing balloon 225 carried on introducer sleeve110 as described further below.

Referring to FIG. 2, the working end 122 includes a flexible, thin-wallmember or structure 150 of a dielectric material that when expanded hasa triangular shape configured for contacting the patient's endometriallining that is targeted for ablation. In one embodiment as shown inFIGS. 2, 5 and 6, the dielectric structure 150 comprises a thin-wallmaterial such as silicone with a fluid-tight interior chamber 152.

In an embodiment, an expandable-collapsible frame assembly 155 isdisposed in the interior chamber. Alternatively, the dielectricstructure may be expanded by a neutral gas without a frame, but using aframe offers a number of advantages. First, the uterine cavity isflattened with the opposing walls in contact with one another. Expandinga balloon-type member may cause undesirable pain or spasms. For thisreason, a flat structure that is expanded by a frame is better suitedfor deployment in the uterine cavity. Second, in embodiments herein, theneutral gas is converted to a conductive plasma at a very low pressurecontrolled by gas inflows and gas outflows—so that any pressurization ofa balloon-type member with the neutral gas may exceed a desired pressurerange and would require complex controls of gas inflows and gasoutflows. Third, as described below, the frame provides an electrode forcontact with the neutral gas in the interior chamber 152 of thedielectric structure 150, and the frame 155 extends into all regions ofthe interior chamber to insure electrode exposure to all regions of theneutral gas and plasma. The frame 155 can be constructed of any flexiblematerial with at least portions of the frame functioning as springelements to move the thin-wall structure 150 from a collapsedconfiguration (FIG. 1) to an expanded, deployed configuration (FIG. 2)in a patient's uterine cavity. In one embodiment, the frame 155comprises stainless steel elements 158 a, 158 b and 160 a and 160 b thatfunction akin to leaf springs. The frame can be a stainless steel suchas 316 SS, 17A SS, 420 SS, 440 SS or the frame can be a NiTi material.The frame preferably extends along a single plane, yet remains thintransverse to the plane, so that the frame may expand into the uterinecavity. The frame elements can have a thickness ranging from about0.005″ to 0.025″. As can be seen in FIGS. 5 and 6, the proximal ends 162a and 162 b of spring elements 158 a, 158 b are fixed (e.g., by welds164) to the distal end 165 of sleeve member 115. The proximal ends 166 aand 166 b of spring elements 160 a, 160 b are welded to distal portion168 of a secondary translatable sleeve 170 that can be extended frombore 175 in translatable sleeve 115. The secondary translatable sleeve170 is dimensioned for a loose fit in bore 175 to allow gas flows withinbore 175. FIGS. 5 and 6 further illustrate the distal ends 176 a and 176b of spring elements 158 a, 158 b are welded to distal ends 178 a and178 b of spring elements 160 a and 160 b to thus provide a frame 155that can be moved from a linear shape (see FIG. 1) to an expandedtriangular shape (FIGS. 5 and 6).

As will be described further below, the bore 175 in sleeve 115 and bore180 in secondary translatable sleeve 170 function as gas outflow and gasinflow lumens, respectively. It should be appreciated that the gasinflow lumen can comprise any single lumen or plurality of lumens ineither sleeve 115 or sleeve 170 or another sleeve, or other parts of theframe 155 or the at least one gas flow lumen can be formed into a wallof dielectric structure 150. In FIGS. 5, 6 and 7 it can be seen that gasinflows are provided through bore 180 in sleeve 170, and gas outflowsare provided in bore 175 of sleeve 115. However, the inflows andoutflows can be also be reversed between bores 175 and 180 of thevarious sleeves. FIGS. 5 and 6 further show that a rounded bumperelement 185 is provided at the distal end of sleeve 170 to insure thatno sharp edges of the distal end of sleeve 170 can contact the inside ofthe thin dielectric wall 150. In one embodiment, the bumper element 185is silicone, but it could also comprise a rounded metal element. FIGS. 5and 6 also show that a plurality of gas inflow ports 188 can be providedalong a length of in sleeve 170 in chamber 152, as well as a port 190 inthe distal end of sleeve 170 and bumper element 185. The sectional viewof FIG. 7 also shows the gas flow passageways within the interior ofintroducer sleeve 110.

It can be understood from FIGS. 1, 2, 5 and 6 that actuation of firstand second handle portions, 114 a and 114 b, (i) initially causesmovement of the assembly of sleeves 115 and 170 relative to bore 120 ofintroducer sleeve 110, and (ii) secondarily causes extension of sleeve170 from bore 175 in sleeve 115 to expand the frame 155 into thetriangular shape of FIG. 5. The dimensions of the triangular shape aresuited for a patient uterine cavity, and for example can have an axiallength A ranging from 4 to 10 cm and a maximum width B at the distal endranging from about 2 to 5 cm. In one embodiment, the thickness C of thethin-wall structure 150 can be from 1 to 4 mm as determined by thedimensions of spring elements 158 a, 158 b, 160 a and 160 b of frameassembly 155. It should be appreciated that the frame assembly 155 cancomprise round wire elements, flat spring elements, of any suitablemetal or polymer that can provide opening forces to move thin-wallstructure 150 from a collapsed configuration to an expandedconfiguration within the patient uterus. Alternatively, some elements ofthe frame 155 can be spring elements and some elements can be flexiblewithout inherent spring characteristics.

As will be described below, the working end embodiment of FIGS. 2, 5 and6 has a thin-wall structure 150 that is formed of a dielectric materialsuch as silicone that permits capacitive coupling of current to engagedtissue while the frame assembly 155 provides structural support toposition the thin-wall structure 150 against tissue. Further, gasinflows into the interior chamber 152 of the thin-wall structure canassist in supporting the dielectric wall so as to contact endometrialtissue. The dielectric thin-wall structure 150 can be free from fixationto the frame assembly 155, or can be bonded to an outward-facing portionor portions of frame elements 158 a and 158 b. The proximal end 182 ofthin-wall structure 150 is bonded to the exterior of the distal end ofsleeve 115 to thus provide a sealed, fluid-tight interior chamber 152(FIG. 5).

In one embodiment, the gas inflow source 140A comprises one or morecompressed gas cartridges that communicate with flexible conduit 136through plug-in connector 137 and receiving connector 138 in the controlunit 135 (FIGS. 1-2). As can be seen in FIGS. 5-6, the gas inflows fromsource 140A flow through bore 180 in sleeve 170 to open terminations 188and 190 therein to flow into interior chamber 152. A vacuum source 145is connected through conduit 136 and connector 137 to allow circulationof gas flow through the interior chamber 152 of the thin-wall dielectricstructure 150. In FIGS. 5 and 6, it can be seen that gas outflowscommunicate with vacuum source 145 through open end 200 of bore 175 insleeve 115. Referring to FIG. 5, it can be seen that frame elements 158a and 158 b are configured with a plurality of apertures 202 to allowfor gas flows through all interior portions of the frame elements, andthus gas inflows from open terminations 188, 190 in bore 180 are free tocirculated through interior chamber 152 to return to an outflow paththrough open end 200 of bore 175 of sleeve 115. As will be describedbelow (see FIGS. 3-4), the gas inflow source 140A is connected to a gasflow or circulation controller 140B which controls a pressure regulator205 and also controls vacuum source 145 which is adapted for assistingin circulation of the gas. It should be appreciated that the frameelements can be configured with apertures, notched edges or any otherconfigurations that allow for effective circulation of a gas throughinterior chamber 152 of the thin-wall structure 150 between the inflowand outflow passageways.

Now turning to the electrosurgical aspects of the invention, FIGS. 5 and6 illustrate opposing polarity electrodes of the system 100 that areconfigured to convert a flow of neutral gas in chamber 152 into a plasma208 (FIG. 6) and to allow capacitive coupling of current through a wall210 of the thin-wall dielectric structure 150 to endometrial tissue incontact with the wall 210. The electrosurgical methods of capacitivelycoupling RF current across a plasma 208 and dielectric wall 210 aredescribed in U.S. patent application Ser. No. 12/541,043; filed Aug. 13,2009 (Atty. Docket No. 027980-000110US) and U.S. application Ser. No.12/541,050 (Atty. Docket No. 027980-000120US), referenced above. InFIGS. 5 and 6, the first polarity electrode 215 is within interiorchamber 152 to contact the neutral gas flow and comprises the frameassembly 155 that is fabricated of an electrically conductive stainlesssteel. In another embodiment, the first polarity electrode can be anyelement disposed within the interior chamber 152, or extendable intointerior chamber 152. The first polarity electrode 215 is electricallycoupled to sleeves 115 and 170 which extends through the introducersleeve 110 to handle 106 and conduit 136 and is connected to a firstpole of the RF source energy source 130A and controller 130B. A secondpolarity electrode 220 is external of the internal chamber 152 and inone embodiment the electrode is spaced apart from wall 210 of thethin-wall dielectric structure 150. In one embodiment as depicted inFIGS. 5 and 6, the second polarity electrode 220 comprises a surfaceelement of an expandable balloon member 225 carried by introducer sleeve110. The second polarity electrode 220 is coupled by a lead (not shown)that extends through the introducer sleeve 110 and conduit 136 to asecond pole of the RF source 130A. It should be appreciated that secondpolarity electrode 220 can be positioned on sleeve 110 or can beattached to surface portions of the expandable thin-wall dielectricstructure 150, as will be described below, to provide suitable contactwith body tissue to allow the electrosurgical ablation of the method ofthe invention. The second polarity electrode 220 can comprise a thinconductive metallic film, thin metal wires, a conductive flexiblepolymer or a polymeric positive temperature coefficient material. In oneembodiment depicted in FIGS. 5 and 6, the expandable member 225comprises a thin-wall compliant balloon having a length of about 1 cm to6 cm that can be expanded to seal the cervical canal. The balloon 225can be inflated with a gas or liquid by any inflation source 148, andcan comprise a syringe mechanism controlled manually or by control unit135. The balloon inflation source 148 is in fluid communication with aninflation lumen 228 in introducer sleeve 110 that extends to aninflation chamber of balloon 225 (see FIG. 7).

Referring back to FIG. 1, the control unit 135 can include a display 230and touch screen or other controls 232 for setting and controllingoperational parameters such as treatment time intervals, treatmentalgorithms, gas flows, power levels and the like. Suitable gases for usein the system include argon, other noble gases and mixtures thereof. Inone embodiment, a footswitch 235 is coupled to the control unit 135 foractuating the system.

The box diagrams of FIGS. 3 and 4 schematically depict the system 100,subsystems and components that are configured for an endometrialablation system. In the box diagram of FIG. 3, it can be seen that RFenergy source 130A and circuitry is controlled by a controller 130B. Thesystem can include feedback control systems that include signalsrelating to operating parameters of the plasma in interior chamber 152of the dielectric structure 150. For example, feedback signals can beprovided from at least one temperature sensor 240 in the interiorchamber 152 of the dielectric structure 150, from a pressure sensorwithin, or in communication, with interior chamber 152, and/or from agas flow rate sensor in an inflow or outflow channel of the system. FIG.4 is a schematic block diagram of the flow control components relatingto the flow of gas media through the system 100 and hand-held device105. It can be seen that a pressurized gas source 140A is linked to adownstream pressure regulator 205, an inflow proportional valve 246,flow meter 248 and normally closed solenoid valve 250. The valve 250 isactuated by the system operator which then allows a flow of a neutralgas from gas source 140A to circulate through flexible conduit 136 andthe device 105. The gas outflow side of the system includes a normallyopen solenoid valve 260, outflow proportional valve 262 and flow meter264 that communicate with vacuum pump or source 145. The gas can beexhausted into the environment or into a containment system. Atemperature sensor 270 (e.g., thermocouple) is shown in FIG. 4 that isconfigured for monitoring the temperature of outflow gases. FIG. 4further depicts an optional subsystem 275 which comprises a vacuumsource 280 and solenoid valve 285 coupled to the controller 140B forsuctioning steam from a uterine cavity 302 at an exterior of thedielectric structure 150 during a treatment interval. As can beunderstood from FIG. 4, the flow passageway from the uterine cavity 302can be through bore 120 in sleeve 110 (see FIGS. 2, 6 and 7) or anotherlumen in a wall of sleeve 110 can be provided.

FIGS. 8A-8D schematically illustrate a method of the invention wherein(i) the thin-wall dielectric structure 150 is deployed within a patientuterus and (ii) RF current is applied to a contained neutral gas volumein the interior chamber 152 to contemporaneously create a plasma 208 inthe chamber and capacitively couple current through the thin dielectricwall 210 to apply ablative energy to the endometrial lining toaccomplish global endometrial ablation.

More in particular, FIG. 8A illustrates a patient uterus 300 withuterine cavity 302 surrounded by endometrium 306 and myometrium 310. Theexternal cervical os 312 is the opening of the cervix 314 into thevagina 316. The internal os or opening 320 is a region of the cervicalcanal that opens to the uterine cavity 302. FIG. 8A depicts a first stepof a method of the invention wherein the physician has introduced adistal portion of sleeve 110 into the uterine cavity 302. The physiciangently can advance the sleeve 110 until its distal tip contacts thefundus 324 of the uterus. Prior to insertion of the device, thephysician can optionally introduce a sounding instrument into theuterine cavity to determine uterine dimensions, for example from theinternal os 320 to fundus 324.

FIG. 8B illustrates a subsequent step of a method of the inventionwherein the physician begins to actuate the first and second handleportions, 114 a and 114 b, and the introducer sleeve 110 retracts in theproximal direction to expose the collapsed frame 155 and thin-wallstructure 150 within the uterine cavity 302. The sleeve 110 can beretracted to expose a selected axial length of thin-wall dielectricstructure 150, which can be determined by markings 330 on sleeve 115(see FIG. 1) which indicate the axial travel of sleeve 115 relative tosleeve 170 and thus directly related to the length of deployed thin-wallstructure 150. FIG. 2 depicts the handle portions 114 a and 114 b fullyapproximated thus deploying the thin-wall structure to its maximumlength.

FIG. 8C illustrates several subsequent steps of a method of theinvention. FIG. 8C first depicts the physician continuing to actuate thefirst and second handle portions, 114 a and 114 b, which furtheractuates the frame 155 (see FIGS. 5-6) to expand the frame 155 andthin-wall structure 150 to a deployed triangular shape to contact thepatient's endometrial lining 306. The physician can slightly rotate andmove the expanding dielectric structure 150 back and forth as thestructure is opened to insure it is opened to the desired extent. Inperforming this step, the physician can actuate handle portions, 114 aand 114 b, a selected degree which causes a select length of travel ofsleeve 170 relative to sleeve 115 which in turn opens the frame 155 to aselected degree. The selected actuation of sleeve 170 relative to sleeve115 also controls the length of dielectric structure deployed fromsleeve 110 into the uterine cavity. Thus, the thin-wall structure 150can be deployed in the uterine cavity with a selected length, and thespring force of the elements of frame 155 will open the structure 150 toa selected triangular shape to contact or engage the endometrium 306. Inone embodiment, the expandable thin-wall structure 150 is urged towardand maintained in an open position by the spring force of elements ofthe frame 155. In the embodiment depicted in FIGS. 1 and 2, the handle106 includes a locking mechanism with finger-actuated sliders 332 oneither side of the handle that engage a grip-lock element against anotch in housing 333 coupled to introducer sleeve 110 (FIG. 2) to locksleeves 115 and 170 relative to introducer sleeve 110 to maintain thethin-wall dielectric structure 150 in the selected open position.

FIG. 8C further illustrates the physician expanding the expandableballoon structure 225 from inflation source 148 to thus provide anelongated sealing member to seal the cervix 314 outward from theinternal os 320. Following deployment of the thin-wall structure 150 andballoon 225 in the cervix 314, the system 100 is ready for theapplication of RF energy to ablate endometrial tissue 306. FIG. 8C nextdepicts the actuation of the system 100, for example, by actuatingfootswitch 235, which commences a flow of neutral gas from source 140Ainto the interior chamber 152 of the thin-wall dielectric structure 150.Contemporaneous with, or after a selected delay, the system's actuationdelivers RF energy to the electrode arrangement which includes firstpolarity electrode 215 (+) of frame 155 and the second polarityelectrode 220 (−) which is carried on the surface of expandable balloonmember 225. The delivery of RF energy delivery will instantly convertthe neutral gas in interior chamber 152 into conductive plasma 208 whichin turn results in capacitive coupling of current through the dielectricwall 210 of the thin-wall structure 150 resulting in ohmic heating ofthe engaged tissue. FIG. 8C schematically illustrates the multiplicityof RF current paths 350 between the plasma 208 and the second polarityelectrode 220 through the dielectric wall 210. By this method, it hasbeen found that ablation depths of three mm to six mm or more can beaccomplished very rapidly, for example in 60 seconds to 120 secondsdependent upon the selected voltage and other operating parameters. Inoperation, the voltage at which the neutral gas inflow, such as argon,becomes conductive (i.e., converted in part into a plasma) is dependentupon a number of factors controlled by the controllers 130B and 140B,including the pressure of the neutral gas, the volume of interiorchamber 152, the flow rate of the gas through the chamber 152, thedistance between electrode 210 and interior surfaces of the dielectricwall 210, the dielectric constant of the dielectric wall 210 and theselected voltage applied by the RF source 130, all of which can beoptimized by experimentation. In one embodiment, the gas flow rate canbe in the range of 5 ml/sec to 50 ml/sec. The dielectric wall 210 cancomprise a silicone material having a thickness ranging from a 0.005″ to0.015 and having a relative permittivity in the range of 3 to 4. The gascan be argon supplied in a pressurized cartridge which is commerciallyavailable. Pressure in the interior chamber 152 of dielectric structure150 can be maintained between 14 psia and 15 psia with zero or negativedifferential pressure between gas inflow source 140A and negativepressure or vacuum source 145. The controller is configured to maintainthe pressure in interior chamber in a range that varies by less than 10%or less than 5% from a target pressure. The RF power source 130A canhave a frequency of 450 to 550 KHz, and electrical power can be providedwithin the range of 600 Vrms to about 1200 Vrms and about 0.2 Amps to0.4 Amps and an effective power of 40 W to 100 W. In one method, thecontrol unit 135 can be programmed to delivery RF energy for apreselected time interval, for example, between 60 seconds and 120seconds. One aspect of a treatment method corresponding to the inventionconsists of ablating endometrial tissue with RF energy to elevateendometrial tissue to a temperature greater than 45 degrees Celsius fora time interval sufficient to ablate tissue to a depth of at least 1 mm.Another aspect of the method of endometrial ablation of consists ofapplying radiofrequency energy to elevate endometrial tissue to atemperature greater than 45 degrees Celsius without damaging themyometrium.

FIG. 8D illustrates a final step of the method wherein the physiciandeflates the expandable balloon member 225 and then extends sleeve 110distally by actuating the handles 114 a and 114 b to collapse frame 155and then retracting the assembly from the uterine cavity 302.Alternatively, the deployed working end 122 as shown in FIG. 8C can bewithdrawn in the proximal direction from the uterine cavity wherein theframe 155 and thin-wall structure 150 will collapse as it is pulledthrough the cervix. FIG. 8D shows the completed ablation with theablated endometrial tissue indicated at 360.

In another embodiment, the system can include an electrode arrangementin the handle 106 or within the gas inflow channel to pre-ionize theneutral gas flow before it reaches the interior chamber 152. Forexample, the gas inflow channel can be configured with axially orradially spaced apart opposing polarity electrodes configured to ionizethe gas inflow. Such electrodes would be connected in separate circuitryto an RF source. The first and second electrodes 215 (+) and 220 (−)described above would operate as described above to provide the currentthat is capacitively coupled to tissue through the walls of thedielectric structure 150. In all other respects, the system and methodwould function as described above.

Now turning to FIGS. 9 and 10, an alternate working end 122 withthin-wall dielectric structure 150 is shown. In this embodiment, thethin-wall dielectric structure 150 is similar to that of FIGS. 5 and 6except that the second polarity electrode 220′ that is exterior of theinternal chamber 152 is disposed on a surface portion 370 of thethin-wall dielectric structure 150. In this embodiment, the secondpolarity electrode 220′ comprises a thin-film conductive material, suchas gold, that is bonded to the exterior of thin-wall material 210 alongtwo lateral sides 354 of dielectric structure 150. It should beappreciated that the second polarity electrode can comprise one or moreconductive elements disposed on the exterior of wall material 210, andcan extend axially, or transversely to axis 111 and can be singular ormultiple elements. In one embodiment shown in more detail in FIG. 10,the second polarity electrode 220′ can be fixed on another lubriciouslayer 360, such as a polyimide film, for example KAPTON®. The polyimidetape extends about the lateral sides 354 of the dielectric structure 150and provides protection to the wall 210 when it is advanced from orwithdrawn into bore 120 in sleeve 110. In operation, the RF deliverymethod using the embodiment of FIGS. 9 and 10 is the same as describedabove, with RF current being capacitively coupled from the plasma 208through the wall 210 and endometrial tissue to the second polarityelectrode 220′ to cause the ablation.

FIG. 9 further shows an optional temperature sensor 390, such as athermocouple, carried at an exterior of the dielectric structure 150. Inone method of use, the control unit 135 can acquire temperature feedbacksignals from at least one temperature sensor 390 to modulate orterminate RF energy delivery, or to modulate gas flows within thesystem. In a related method of the invention, the control unit 135 canacquire temperature feedback signals from temperature sensor 240 ininterior chamber 152 (FIG. 6 to modulate or terminate RF energy deliveryor to modulate gas flows within the system.

In another aspect of the invention, FIG. 11 is a graphic representationof an algorithm utilized by the RF source 130A and RF controller 130B ofthe system to controllably apply RF energy in an endometrial ablationprocedure. In using the expandable dielectric structure 150 of theinvention to apply RF energy in an endometrial ablation procedure asdescribed above, the system is configured to allow the dielectricstructure 150 to open to different expanded dimensions depending on thesize and shape of the uterine cavity 302. The axial length of dielectricstructure 150 also can be adjusted to have a predetermined axial lengthextended outward from the introducer sleeve 110 to match a measuredlength of a uterine cavity. In any case, the actual surface area of theexpanded dielectric structure 150 within different uterine cavities willdiffer—and it would be optimal to vary total applied energy tocorrespond to the differing size uterine cavities.

FIG. 11 represents a method of the invention that automaticallydetermines relevant parameters of the tissue and the size of uterinecavity 302 to allow for selection of an energy delivery mode that iswell suited to control the total applied energy in an ablationprocedure. In embodiments, RF energy is applied at constant power for afirst time increment, and the following electrical parameters (e.g.,voltage, current, power, impedance) are measured during the applicationof energy during that first time increment. The measured electricalparameters are then used (principally, power and current, V=P/I) todetermine a constant voltage to apply to the system for a second timeinterval. The initial impedance may be also be utilized by thecontroller as a shutoff criteria for the second treatment interval aftera selected increase in impedance.

For example, in FIG. 11, it can be seen that a first step following thepositioning of the dielectric structure in the uterine cavity 302 is toapply radiofrequency energy in a first mode of predetermined constantpower, or constant RF energy (“FIRST MODE-POWER”). This first power issufficient to capacitively couple current across the dielectric tocontacted tissue, wherein empirical studies have shown the power can bein the range of 50 W-300 W, and in one embodiment is 80 W. This firstpower mode is applied for a predetermined interval which can be lessthan 15 seconds, 10 seconds, or 5 seconds, as examples, and is depictedin FIG. 11 as being 2 seconds. FIG. 11 shows that, in accordance withembodiments, the voltage value is determined a voltage sensor incontroller 130A and is recorded at the “one-second” time point after theinitiation of RF energy delivery. The controller includes a powersensor, voltage sensor and current sensor as is known in the art. Thisvoltage value, or another electrical parameter, may be determined andrecorded at any point during the interval, and more than one recordingmay be made, with averages taken for the multiple recordings, or themultiple recordings may be used in another way to consistently take ameasurement of an electrical value or values. FIG. 11 next illustratesthat the controller algorithm switches to a second mode (“SECONDMODE-VOLTAGE”) of applying radiofrequency energy at a selected constantvoltage, with the selected constant voltage related to the recordedvoltage (or other electrical parameter) at the “one-second” time point.In one embodiment, the selected constant voltage is equal to therecorded voltage, but other algorithms can select a constant voltagethat is greater or lesser than the recorded voltage but determined by afactor or algorithm applied to the recorded voltage. As further shown inFIG. 11, the algorithm then applies RF energy over a treatment intervalto ablate endometrial tissue. During this period, the RF energy isvaried as the measured voltage is kept constant. The treatment intervalcan have an automatic time-out after a predetermined interval of lessthat 360 seconds, 240 seconds, 180 seconds, 120 seconds or 90 seconds,as examples.

By using the initial delivery of RF energy through the dielectricstructure 150 and contacted tissue in the first, initial constant powermode, a voltage level is recorded (e.g., in the example, at one second)that directly relates to a combination of (i) the surface area of thedielectric structure, and the degree to which wall portions of thedielectric structure have been elastically stretched; (ii) the flow rateof neutral gas through the dielectric structure and (iii) the impedanceof the contacted tissue. By then selecting a constant voltage for thesecond, constant voltage mode that is directly related to the recordedvoltage from the first time interval, the length of the second,treatment interval can be the same for all different dimension uterinecavities and will result in substantially the same ablation depth, sincethe constant voltage maintained during the second interval will resultin power that drifts off to lower levels toward the end of the treatmentinterval as tissue impedance increases. As described above, thecontroller 130A also can use an impedance level or a selected increasein impedance to terminate the treatment interval.

The algorithm above provides a recorded voltage at set time point in thefirst mode of RF energy application, but another embodiment can utilizea recorded voltage parameter that can be an average voltage over ameasuring interval or the like. Also, the constant voltage in the secondmode of RF energy application can include any ramp-up or ramp-down involtage based on the recorded voltage parameter.

In general, an electrosurgical method for endometrial ablation comprisespositioning a RF ablation device in contact with endometrial tissue,applying radiofrequency energy in a first mode based on a predeterminedconstant power over a first interval, and applying radiofrequency energyin a second mode over a second interval to ablate endometrial tissue,the energy level of the second mode being based on treatment voltageparameters obtained or measured during the first interval. Power duringthe first interval is constant, and during the second period is variedto maintain voltage at a constant level. Another step in applying RFenergy in the first mode includes the step of recording a voltageparameter in the first interval, wherein the voltage parameter is atleast one of voltage at a point in time, average voltage over a timeinterval, and a change or rate of change of voltage. The second modeincludes setting the treatment voltage parameters in relation to thevoltage parameter recorded in the first interval.

Referring to FIG. 11, it can be understood that an electrosurgicalsystem for endometrial ablation comprises a radiofrequency ablationdevice coupled to an radiofrequency power supply, and control meansconnected to the radiofrequency power supply for switching theapplication of radiofrequency energy between a constant power mode and aconstant voltage mode. The control means includes an algorithm that (i)applies radiofrequency energy in the first mode (ii) records the voltagewithin a predetermined interval of the first mode, and (iii) appliesradiofrequency energy in the second mode with constant voltage relatedto the recorded voltage.

In another aspect, the invention comprises a radiofrequency powersupply, a means for coupling the radiofrequency power supply to anablation device configured for positioning in a uterine cavity, theablation device comprising a dielectric for contacting endometrialtissue, a system for recording an electrical parameter of the ablationdevice and contacted tissue, and a feedback system for varying theapplication of radiofrequency energy to tissue between a constant powermode and a constant voltage mode based on a recorded electricalparameter.

Although particular embodiments of the present invention have beendescribed above in detail, it will be understood that this descriptionis merely for purposes of illustration and the above description of theinvention is not exhaustive. Specific features of the invention areshown in some drawings and not in others, and this is for convenienceonly and any feature may be combined with another in accordance with theinvention. A number of variations and alternatives will be apparent toone having ordinary skills in the art. Such alternatives and variationsare intended to be included within the scope of the claims. Particularfeatures that are presented in dependent claims can be combined and fallwithin the scope of the invention. The invention also encompassesembodiments as if dependent claims were alternatively written in amultiple dependent claim format with reference to other independentclaims.

1. A method of endometrial ablation, comprising: positioning a workingend of an RF ablation device in a patient uterus to contact endometrialtissue, the working end comprising a dielectric; applying radiofrequencyenergy for a first interval of time at constant power, the power beingsufficient to capacitively couple current across the dielectric to thecontacted endometrial tissue; recording a voltage parameter within thefirst interval; and applying radiofrequency energy at a constant voltageover a second, treatment interval to ablate endometrial tissue, theconstant voltage being related to the recorded voltage.
 2. The method ofclaim 1, wherein the first interval is less than 15 seconds.
 3. Themethod of claim 1, wherein the first interval is less than 10 seconds.4. The method of claim 1, wherein the first interval is less than 5seconds.
 5. The method of claim 1, wherein the voltage parametercomprises a recorded voltage measured at a single point in time duringthe first interval.
 6. The method of claim 1, wherein the voltageparameter comprises multiple recorded voltages taken during the firstinterval and averaged.
 7. The method of claim 1, wherein the constantvoltage is equal to the voltage parameter.
 8. The method of claim 1,wherein the constant voltage is greater than the voltage parameter. 9.The method of claim 1, wherein the constant voltage is less than thevoltage parameter.
 10. The method of claim 1, wherein the constantvoltage includes a ramp-up of voltage.
 11. The method of claim 1,wherein the constant voltage includes a ramp-down of voltage.
 12. Amethod of endometrial ablation, comprising: positioning a working end ofan RF ablation device in a patient uterus to contact endometrial tissuein the uterus; applying radiofrequency energy at constant power during afirst time interval; recording an electrical parameter within the firsttime interval; and applying radiofrequency energy at a constant voltageover a second, treatment time interval to ablate endometrial tissue, theconstant voltage being derived from the electrical parameter.
 13. Themethod of claim 12, wherein the electrical parameter comprises a voltageparameter.
 14. The method of claim 13, wherein the voltage parametercomprises a recorded voltage measured at a single point in time duringthe first interval.
 15. The method of claim 14, wherein the voltageparameter comprises multiple recorded voltages taken during the firstinterval and averaged.
 16. The method of claim 12, wherein the constantvoltage is equal to the voltage parameter.
 17. The method of claim 12,wherein the constant voltage is greater than the voltage parameter. 18.The method of claim 12, wherein the constant voltage is less than thevoltage parameter.
 19. The method of claim 12, wherein the constantvoltage includes a ramp-up of voltage.
 20. The method of claim 12,wherein the constant voltage includes a ramp-down of voltage.
 21. Anelectrosurgical method for endometrial ablation, comprising: positioninga RF ablation device in contact with endometrial tissue in a patient;applying radiofrequency energy in a first mode at constant power over afirst interval; and applying radiofrequency energy in a second mode overa second interval to ablate endometrial tissue, the energy level of thesecond mode being determined based on an electrical parameter obtainedfrom the first mode.
 22. The method of claim 21, wherein the electricalparameter comprises a voltage parameter recorded in the first interval.23. The method of claim 22, wherein the voltage parameter comprises arecorded voltage measured at a single point in time during the firstinterval.
 24. The method of claim 22, wherein the voltage parametercomprises multiple recorded voltages taken during the first interval andaveraged.
 25. The method of claim 22, wherein the voltage parametercomprises a change in voltage over the first interval.
 26. The method ofclaim 22, wherein the voltage parameter comprises a rate of change ofvoltage over the first interval.
 27. The method of claim 22, wherein theenergy level of the second mode being determined based on an electricalparameter obtained from the first mode comprises setting a voltageparameter of the second mode in relation to the electrical parameter.28. The method of claim 26, wherein setting the voltage parametercomprises setting a constant voltage.
 29. The method of claim 26,wherein setting the voltage parameter comprises setting a ramp-up involtage.
 30. The method of claim 26, wherein setting the voltageparameter comprises setting a ramp-down in voltage.
 31. Anelectrosurgical system for endometrial ablation, comprising: aradiofrequency ablation device coupled to an radiofrequency powersupply; and a controller connected to the radiofrequency power supplyand configured to operate the radiofrequency power supply by switchingthe application of radiofrequency energy to the ablation device betweena first, constant power mode and a second, constant voltage mode. 32.The electrosurgical system of claim 31 wherein the controller isconfigured to (i) apply radiofrequency energy in the first mode (ii)record a voltage parameter during the first, and (iii) appliesradiofrequency energy in the second mode at constant voltage related tothe recorded voltage parameter.
 33. The electrosurgical system of claim32, wherein the voltage parameter comprises a recorded voltage measuredat a single point in time during the first mode.
 34. The electrosurgicalsystem of claim 32, wherein the voltage parameter comprises multiplerecorded voltages taken during the first interval and averaged.
 35. Theelectrosurgical system of claim 32, wherein the voltage parametercomprises a change in voltage over the first interval.
 36. Theelectrosurgical system of claim 32, wherein the voltage parametercomprises a rate of change of voltage over the first interval.
 37. Anelectrosurgical system for endometrial ablation, comprising: aradiofrequency ablation device coupled to an RF power supply; controlmeans connected to the radiofrequency power supply for switching theapplication of radiofrequency energy to the ablation device between aconstant power mode and a variable power mode.
 38. The electrosurgicalsystem of claim 37, wherein the control means operates the variablepower mode to maintain a constant voltage.
 39. An electrosurgical systemfor endometrial ablation, comprising: an ablation device configured forpositioning in a uterine cavity, the ablation device comprising adielectric for contacting endometrial tissue; a radiofrequency powersupply coupled to the ablation device; a system for recording anelectrical parameter of the ablation device and contacted tissue; and afeedback system coupled to the radiofrequency power supply for varyingthe application of radiofrequency energy provided by the radiofrequencypower supply to the ablation device between a constant power mode and aconstant voltage mode, the constant voltage mode being based on anelectrical parameter measured by the system for recording during theconstant power mode.
 40. The electrosurgical system of claim 39, whereinthe electrical parameter comprises a voltage parameter.
 41. Theelectrosurgical system of claim 40, wherein the voltage parametercomprises a recorded voltage measured at a single point in time duringthe first mode.
 42. The electrosurgical system of claim 40, wherein thevoltage parameter comprises multiple recorded voltages taken during thefirst interval and averaged.
 43. The electrosurgical system of claim 40,wherein the voltage parameter comprises a change in voltage over thefirst interval.
 44. The electrosurgical system of claim 40, wherein thevoltage parameter comprises a rate of change of voltage over the firstinterval.